1. Field of the Invention
The present invention relates to a hub assembly, and more particularly to a hub assembly for a disk brake of a bicycle.
2. Description of the Related Art
A conventional hub assembly for a disk brake of a bicycle in accordance with the prior art shown in FIGS. 6 and 7 comprises a support shaft 50 secured to a seat stay or chain stay (not shown), a hub body 60 pivotally mounted on the support shaft 50 and provided with two drum disks 61 for mounting spokes (not shown), a chainwheel 80 mounted on one of the two drum disks 61 of the hub body 60, a mounting portion 62 protruding from the other one of the two drum disks 61 of the hub body 60 and having a periphery provided with a plurality of protruding blocks 63 each formed with an insertion hole 64, a brake disk 70 mounted on the mounting portion 62 and having a periphery provided with a plurality of protruding plates 75 each resting on the respective protruding block 63 and each formed with a through hole 76, and an urging cap 65 resting on the brake disk 70 and having a periphery provided with a plurality of inserts 66 each extended through the through hole 76 of the respective protruding plate 75 of the brake disk 70 and each inserted into the insertion hole 64 of the respective protruding block 63 to press the brake disk 70 on the hub body 60.
When the brake disk 70 is subjected to a braking force applied by a disk brake (not shown) of the bicycle, the braking force applied on the brake disk 70 is distributed to the mounting portion 62 of the hub body 60 and the urging cap 65. However, the inserts 66 of the urging cap 65 are loosely fit in the insertion holes 64 of the protruding blocks 63, so that the urging cap 65 is easily loosened, and the braking force is concentrated on the inserts 66 of the urging cap 65. Thus, the inserts 66 of the urging cap 65 are easily worn or broken due to a stress concentration, thereby decreasing the lifetime of the hub assembly. On the other hand, when the inserts 66 of the urging cap 65 are closely fit in the insertion holes 64 of the protruding blocks 63, the inserts 66 of the urging cap 65 are easily jammed with the insertion holes 64 of the protruding blocks 63, so that the urging cap 65 cannot removed from the hub body 60 easily.